Optical pickup and information device for reducing an influence of stray light in an information recording medium

1. An optical pickup for recording or reproducing an information signal with respect to an optical disc comprising a plurality of recording layers, each recording layer having a recording track in which information pits are arranged, the information signal being recorded in the information pits, the optical pickup comprising: a light source for irradiating a laser beam; a diffracting device for diffracting the irradiated laser beam; an optical system for guiding the diffracted laser beam to one recording layer of the plurality of recording layers; an optical element for changing (i) a polarization direction in at least one portion of signal light generated in the one recording layer and (ii) a polarization direction in at least one portion of stray light generated in another recording layer of the plurality of recording layers, if the guided laser beam is focused on the one recording layer; and a plurality of light receiving devices for respectively receiving zero-order light, +first-order diffraction light and −first-order diffraction light, wherein one portion of the optical element sets the polarization direction in the one portion of the signal light and the one portion of the stray light to a first direction, and another portion of the optical element sets the polarization direction in another portion of the signal light and another portion of the stray light to a second direction, the light receiving devices are arranged so as to receive the one portion of the signal light with the another portion of the stray light, shapes of the one portion and the another portion of the optical element and a relative positional relationship between the one portion and the another portion of the optical element are defined on the basis of a width of a dead band which reduces an influence of a light interference of the signal light and the stray light, in an optical diameter of the signal light, and the optical element is disposed in a position in which optical diameters of a plurality of stray lights, generated in a plurality of recording layers other than the one recording layer, are all substantially equal, on an optical axis.

2. The optical pickup according to claim 1 , wherein the signal light is signal light of zero-order light or signal light of ±first-order diffraction light, and the stray light is stray light of zero-order light or stray light of ±first-order diffraction light.

3. The optical pickup according to claim 1 , wherein the first direction and the second direction are dissimilar in polarization direction by 90 degrees.

4. The optical pickup according to claim 1 , wherein either the one portion of the optical element or the another portion of the optical element is a λ/2 wavelength plate.

5. The optical pickup according to claim 1 , wherein the optical element is disposed on an optical path in which return light, which is generated in the plurality of recording layers, is guided to the light receiving devices.

6. The optical pickup according to claim 1 , wherein the optical element is disposed in a vicinity of a position on an irradiation side, of two focal lines of the signal light based on an astigmatic method.

7. The optical pickup according to claim 1 , wherein shapes of the one portion and the another portion of the optical element and a relative positional relationship between the one portion and the another portion of the optical element are defined on the basis of (i-1) an optical diameter or optical magnification of the signal light corresponding to zero-order light on a plane perpendicular to an optical axis and (i-2) an optical diameter or optical magnification of the stray light, (ii-1) an optical diameter, a beam position, or optical magnification of the signal light corresponding to ±first-order light on the plane perpendicular to the optical axis, and (ii-2) an optical diameter, a beam position, or optical magnification of the stray light.

8. The optical pickup according to claim 1 , wherein shapes of the one portion and the another portion of the optical element and a relative positional relationship between the one portion and the another portion of the optical element are defined on the basis of an interference pattern between the signal light and the stray light on the light receiving devices.

9. The optical pickup according to claim 8 , wherein the optical pickup further comprises a cylindrical lens for performing an astigmatic method, and the optical element is defined on the basis of the interference pattern on the light receiving devices, which is specified by (i) an angle between a diffraction direction of a +first-order light component of the signal light and a diffraction direction of a −first-order light component of the signal light and (ii) a cylinder direction of the cylindrical lens.

10. The optical pickup according to claim 1 , wherein the optical element has at least two of the one portion of the optical element and at least two of the another portion of the optical element, which have a linear-symmetric positional relationship on the basis of a direction of a focal line corresponding to zero-order light.

11. The optical pickup according to claim 1 , wherein the optical element has at least two of the one portion of the optical element and at least two of the another portion of the optical element, which have a linear-symmetric positional relationship on the basis of a direction for light-receiving a push-pull signal.

12. The optical pickup according to claim 1 , wherein the optical pickup further comprises a hologram element for at least changing a focal position of the signal light or a focal position of the stray light, and the hologram element changes the focal position such that (i) the one portion of the signal light and the another portion of the stray light or (ii) the another portion of the signal light and the one portion of the stray light are received together by the light receiving devices.

13. The optical pickup according to claim 1 , wherein the optical element makes the polarization direction of the signal light corresponding to ±first-order diffraction light, be different from the polarization direction of the stray light corresponding to zero-order light, and among (i) a first light receiving device for receiving the zero-order light, (ii) a second light receiving device for receiving a +first-order diffraction light, and (iii) a third light receiving device for receiving a −first-order diffraction light, the light receiving devices include at least the second light receiving device and the third light receiving device.

14. The optical pickup according to claim 1 , further comprising a controlling device for controlling the optical system to guide the laser beam to the recording track provided for the one recording layer, on the basis of the received signal light.

15. An information equipment comprising: an optical pickup; and a recording/reproducing device for irradiating an optical disc with a laser beam, to thereby perform a recording or reproduction of an information signal, wherein the optical pickup is for recording or reproducing the information signal with respect to the optical disc comprising a plurality of recording layers, each recording layer having a recording track in which information pits are arranged, the information signal being recorded in the information pits, the optical pickup comprising: a light source for irradiating a laser beam; a diffracting device for diffracting the irradiated laser beam; an optical system for guiding the diffracted laser beam to one recording layer of the plurality of recording layers; an optical element for changing (i) a polarization direction in at least one portion of signal light generated in the one recording layer and (ii) a polarization direction in at least one portion of stray light generated in another recording layer of the plurality of recording layers, if the guided laser beam is focused on the one recording layer; and a plurality of light receiving devices for respectively receiving zero-order light, +first-order diffraction light and −first-order diffraction light, wherein one portion of the optical element sets the polarization direction in the one portion of the signal light and the one portion of the stray light to a first direction, and another portion of the optical element sets the polarization direction in another portion of the signal light and another portion of the stray light to a second direction, the light receiving devices are arranged so as to receive the one portion of the signal light with the another portion of the stray light, shapes of the one portion and the another portion of the optical element and a relative positional relationship between the one portion and the another portion of the optical element are defined on the basis of a width of a dead band which reduces an influence of a light interference of the signal light and the stray light, in an optical diameter of the signal light, and the optical element is disposed in a position in which optical diameters of a plurality of stray lights, generated in a plurality of recording layers other than the one recording layer, are all substantially equal, on an optical axis.